Effect of Colour Centres on the Cr3+ Spectrum in Ruby

It is found that the colour centres in ruby cause an increase of the oscillator strength in the transitions corresponding to the R‐ and B‐lines of the Cr3+ absorption and a decrease of the relaxation time τ of the luminescence in the R‐lines. These effects can be explained by a partial forbiddenness violation for the transitions 4A2 → 2E and 4A2 → 2T2 induced by the change in the intercrystalline field due to the charged colour centres (by Cr2+ and Cr4+ ions). From the broadening of the ESR lines the effective field due to the colour centres is estimated.